Transcript of "Bronze"

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BRONZE-INTRODUCTION
 Bronze is an alloy consisting primarily of copper, usually
with tin as the main additive.
 Bronze now refers to alloy of copper having elements of silicon,
manganese etc which may or may not have zinc.
 The discovery of bronze enabled people to create metal objects
which were better than previously possible.(Bronze age – 2nd
cent. B.C)
 Tools, weapons, armor, and various building materials, like
decorative tiles, made of bronze were harder and more durable
than their stone and copper predecessors.
 Initially bronze was made out of copper and arsenic to
form arsenic bronze.
 It was only later that tin was used, becoming the sole type of
bronze in the late 3rd millennium BC.
 Tin bronze was superior to arsenic bronze in that the alloying
process itself could more easily be controlled and the alloy was
stronger and easier to cast.Also, unlike arsenic, tin is not toxic.
Ewer from 7th century Iran. Cast,
chased, and inlaid bronze. New York
Metropolitan Museum of Art
A large bronze cast medallion of the 16th
century.Chinese sword made of bronze

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 "True" bronze is a combination of approximately 88% copper (Cu) and 12% tin (Sn),
however there are three major classes or types of "bronzes" used in sculpture and
construction.
 They are:
1. Statuary Bronze - approximately 97% copper (Cu), 2% tin(Sn) and 1% zinc (Zn); this
composition is the closest to "true" bronze.
2. Architectural Bronze - actually more of a "leaded brass“, is commonly composed of
approximately 57% copper (Cu), 40% zinc (Zn) and 3% lead (Pb).
3. Commercial Bronze - composed of approximately 90% copper(Cu) and 10% zinc
(Zn).
 Aluminium bronze - aluminium is the main alloying metal added to copper. Aluminium
bronzes are most commonly used in applications where their resistance to corrosion makes
them preferable to other engineering materials. These applications include plain bearings
and landing gear components on aircraft, engine components (especially for seagoing ships),
underwater fastenings
TYPES OF BRONZE

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PROPERTIES
 The bronzes are generally as strong as they are alloys.
 They are tough and ductile at all temperatures and retain their strength well at elevated
temperatures.
 extremely malleable and durable.
 Melts at 950 centigrade.
 Resists corrosion (especially seawater corrosion-is due to the formation of an intrinsic, thin
but tough adherent film of aluminium oxide.)
 Metal fatigue more than steel.
 Better conductor of heat and electricity.
 Bronze in its "raw" state is a "pinkish", salmon colored metal, however it is rarely seen in its
pure state.
 Bronze usually exhibits some patination or corrosion so that its color normally ranges
from dark brown to lime green.
 Exposed bronze undergoes continuous change and progresses through several predictable
"stages" of oxidation and corrosion.
 It is also non-sparking, so it is often used to make tools for use in combustible
environments.
 Its resonance also makes it ideal for use in casting bells.
 It causes minimal friction, making it highly useful for machine parts and other
applications that involve metal-on-metal contact, such as gears.

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USES
 Bronze is commonly used in ship propellers and submerged bearings owing to its
combination of toughness and resistance to salt water corrosion.
 It is also widely used for cast bronze sculpture. Many common bronze alloys have the
unusual and very desirable property of expanding slightly just before they set, thus filling in
the finest details of a mold.
 Phosphor bronze is particularly suited to precision-grade bearings clips, electrical
connectors and springs. It is also used in guitar and piano strings.
 It is used to make hammers, mallets, wrenches and other durable tools to be used in
explosive atmospheres or in the presence of flammable vapors.
 Bronze is used to make bronze wool for woodworking applications where steel
wool would discolor oak.
 Bronze is the preferred metal for top-quality bells
 Bronze has been used in the manufacture of various types of medals
 Architectural bronze is typically used for:
1.door and window frames
2.doorand window hardware
3. rails,
4. furniture hardware.

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a small section of the bronze frieze that runs
all the way round the Chanin Building.
The Bronze Tiger of Mysore
Mysore Palace has six of these magnificent scupltures in and around
the grand Mysore Palace
Elias & Co. Department Store Bronze coating glasses in a building

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a small section of the bronze frieze that runs
all the way round the Chanin Building.
The Bronze Tiger of Mysore
Mysore Palace has six of these magnificent scupltures in and around
the grand Mysore Palace
Elias & Co. Department Store Bronze coating glasses in a building

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APPLICATIONS
1. MARINE
The outstanding corrosion resistance of Aluminium Bronze in marine environments coupled
with its high strength and wear resistance, have made it a first choice for ships' propellers for
many years. Modern vessels are fitted with smaller variable pitch propellers and these are
cast in Aluminium Bronze as are the associated gearboxes.Aluminium Bronze is widely used
for pumps, valves and pipes on oil and gas platforms.
Typical component being machined
Impeller in aluminium bronze
Unit under construction –
aluminium bronze components
clearly visible
ALUMINIUMBRONZE

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WELDING
•All Aluminium Bronzes can be welded, whether in cast or wrought form.
•it is possible to manufacture components by the most economic production techniques.
•In the event of damage, it is also possible to repair aluminium bronze components by
welding, frequently while still in place.
•INERT GAS SHIELDED ARC WELDING is generally recommended.
•An electric arc forms between a consumable wire (tungsten)electrode and the work piece
metal(s), which heats the work piece metal(s), causing them to melt, and join. Along with the
wire electrode, a shielding gas(argon or helium) feeds through the welding gun, which
shields the process from contaminants in the air.
(1) Direction of travel, (2) Contact
tube,(3) Electrode, (4) Shielding
gas, (5) Molten weld metal, (6)Solidified
weld metal, (7) Workpiece.

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2. BUILDING AND CONSTRUCTION
The entire weight of this dome roof at Aberdeen
University,Scotland is supported on Aluminium
Bronze spherical joints set in concrete.
Many modern buildings and large bridges
use Aluminium Bronze expansion joints,
masonry fixings

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3. GENERAL ENGINEERING
Aluminium Bronze components are found in many general engineering
applications where high strength coupled with wear and corrosion
resistance is required.
The non-galling property is an added advantage Rolls
Royce appreciate when they specify aluminium
bronze for their wheel nuts
Gear wheels for British Rail braking systems are cast in
aluminium bronze

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A rich variety of shapes
•The ease with which architectural bronze can be formed
opens up enormous design possibilities for window frames,
façades and door sections.
•Architectural bronze can be formed by various techniques.
•The processes:
casting – hot extrusion – cold forming
•All aluminium or stainless steel section shapes can be
produced in bronze
•Wall thicknesses range from 1.0 to 4.0 mm.
SOURCE - www.swissmetal.com

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PROBLEMS AND DEFECTS
•Bronze usually exhibits some patination or corrosion so that its color normally ranges from lime green to
dark brown. Exposed bronze undergoes continuous change and progresses through several predictable
"stages" of oxidation and corrosion.
•The stages of bronze corrosion vary in duration and time of onset, based on many factors, including:
1. composition of the bronze
2. patination or other protective treatments applied
3. weather
4. location and exposure to rain, sun, and other climatic conditions
5. atmospheric pollutants
6. scheduled maintenance/cleaning, and
7. adjacent materials including residual core materials.
•Problems may be classified into two broad categories:
1) Natural or inherent problems based on the characteristics of the material and the conditions of
the exposure
2) Mechanical deterioration

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PATINATION
•Patina is defined as a film or layer caused by oxidisation of old bronze.
•In nature this occurs over a long period of time and can result in a variety of interesting colours usually
green.
•With the use of a variety of chemicals and processes carried out in factory, the outcome can be accelerated
and controlled.
•The process can produce an interesting range of patinas giving a more natural appearance. They are often
selected for historical or artistic work.
•Artificial patinas are applied to bronze using chemical solutions which react with the surface to form a thin
layer of coloured corrosion products.
•Patinas can be transparent or opaque and are sometimes applied in a number of layers to produce widely
varied effects.

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•Bronze Oil Rubbed: there is no rubbing to bring out the bronze color. Some bronze
color shows through and more will show over time with wear.
•Bronze with Patina: Heavy application of black patina which gives a bold contrast and
accentuates the carved design.Top surface is buffed to bring out the Bronze color.
•Bronze Raw: Raw bronze is cast and sold without any touching of the surface. There is
major color variation of black to copper which cannot be controlled. Raw Bronze has a
distinct “Old World” look and feel.The surface, in some areas, may be rough.
•Bronze no Patina: Bronze is poured, cleaned and buffed. Depending upon the depth of
the design; you might get some dark areas.

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NATURAL PROBLEMS
1. CORROSION :
 the existence of chemicals in the atmosphere, such as chlorine, sulfur, and nitrogen oxides, in the presence of
moisture, is the most significant cause of bronze deterioration.
Corrosion may have many causes and symptoms, including:
1. Uniform oxidation or corrosion or patination: Corrosion attacks the metal surface evenly.
2. Pitting: Attacks the metal surface in localized areas
Sulphide pollution of the sea water may cause pitting in most copper alloys including aluminium bronzes
3. Selective attack: When a metal is not homogenous throughout, certain areas may be attacked in
preference to others.
4. Erosion: When a corrosion-resistant oxide layer is removed and the bare metal beneath corrodes.
Erosion in the bronze layer underneath
chromium playing, which has peeled offPitting of bronzeOxidation of bronze

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5. Stress corrosion cracking: Attacks areas in a metal which were stressed during metal working.
6. Humidity, temperature and condensation: Affect the rate of corrosion; in a marine environment,
aerosols can deposit chloride and other salts which will accelerate the rate of atmospheric corrosion.
7. Bronze disease: Bronze disease is the result of exposure to chlorine compounds which can come
from any saline source, such as contact with saline soils, atmospheric pollutants or airborne salt spray
near bodies of salt water. The chlorine reacts with the copper in bronze to form copper chloride. The
copper chloride is relatively unstable and the only way to arrest the continuing corrosion is the complete
removal of the chlorides using electrochemical methods.
Stress corrosion cracking
Bronze disease

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1. Abrasion:
• Causes removal of the protective metal surface. Some metals such as zinc are relatively soft and
therefore vulnerable to abrasion damage.
2. Fatigue:
•Failure of metal that has been repeatedly stressed beyond its elastic limit, due to failure to
provide necessary allowances for thermal expansion and contraction caused by temperature
differences.
3.Heat:
•Usually in the form of fire, will cause many metals to become plastic, distort, and fail.
4.Distortion:
•Permanent deformation or failure may occur when a metal is overloaded beyond its yield point
because of increased live or dead loads, thermal stresses, or structural modifications altering a
stress regime.
MECHANICAL DETERIORATION
(PURELY PHYSICAL PROCESSES):

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DISADVANTAGES OF BRONZE
 More expensive than steel, brass more likely to crack under load.
 It is a heavy metal
 Like copper, bronze can develop a patina, a green film as a result of long exposure to moist air.
 Bronze will deteriorate rapidly if exposed to moisture and chlorides or sulfides.
 Bronze is susceptible to “Bronze Disease “one of the most serious hazards of bronze.
ADVANTAGES OF BRONZE
 It won't rust but it'll develop a pleasant patina over time
 Corrosion Resistance - By forming a protective surface film, most copper alloys resist many
corrosive environments
 Withstand High Temperatures - Several families of bronze alloys work well in elevated
temperature environments
 Friction and Wear - Copper alloys wear well against steel and are used in numerous bearing and
gear components
 Good Machinability - In general, copper alloys are easy to machine compared to steel
 Weldability - Many grades can be welded
 Brazing and Soldering - All grades of copper alloys can be brazed and soldered

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 The use of extruded bronze mullions and
bronze spandrels together with a dark amber-
tinted glass has unified the surface with color.
 Unbroken height of bronze
 Bronze I-beams ready to ship from chicago’s
extruded metals company to new york city,
where they will be part of the construction of
the new seagram’s building tower in midtown,
1956.
CASE STUDY-1
SEAGRAM BUILDING(NEWYORK)
Seagram building

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CASE STUDY-2
WARRINGTON PLACE,DUBLIN,IRELAND
 This composition is contained by the over sailing
bronze canopy roof.
 The entrance forecourt balances the fluid bronze
sculpture by Michael Warren.
 Roof ,cladding elements and a fluid sculpture all
formed from bronze.
 This material –sourced in Germany fabricated in Italy
and treated with bees-wax to maintain its natural
luster adds a distinctive quality to the building
appearance .
Bronze was chosen
 To add a civic quality to the building façade
 Providing visual interest and a unique signature for the
building.
 Elevation treatment. Warrington place